Overview

Neuropsychological evaluation (NPE) is a testing method through which a neuropsychologist can acquire data about a subject’s cognitive, motor, behavioral, linguistic, and executive functioning. In the hands of a trained neuropsychologist, these data can provide information leading to the diagnosis of a cognitive deficit or to the confirmation of a diagnosis, as well as to the localization of organic abnormalities in the central nervous system (CNS). The data can also guide effective treatment methods for the rehabilitation of impaired patients.

NPE provides insight into the psychological functioning of an individual, a capacity for which modern imaging techniques
[1, 2] have only limited ability. However, these tests must be interpreted by a trained, experienced neuropsychologist in order to be of any benefit to the patient. These tests are often coupled with information from clinical reports, physical examination, and increasingly, premorbid and postmorbid self and relative reports. Alone, each neuropsychological test has strengths and weaknesses in its validity, reliability, sensitivity, and specificity. However, through eclectic testing and new in situ testing, the utility of NPE is increasing dramatically.
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Major Domains of Neuropsychological Functioning

NPE is useful for measuring many function categories, including the following:

Referrals for Neuropsychological Evaluation

NPE is used to quantitatively measure the cognitive and behavioral capabilities of a patient. The data from neuropsychological tests can then be compared with normative data based on a number of different demographic criteria, including (but not limited to) age, race, gender, and socioeconomic status. NPE can include testing of intelligence, attention, memory, and personality, as well as of problem solving, language, perceptual, motor, academic, and learning abilities.

Whom to refer for NPE

Neuropsychological testing provides diagnostic clarification and grading of clinical severity for patients with obvious or supposed cognitive deficits. Often these include patients with a history of any of the following problems:

NPE is of limited value if a patient is severely compromised, as in advanced dementia or early in recovery from serious brain injury (eg, TBI, stroke, anoxia, infection), although brief serial assessment with measures such as the Galveston Orientation and Amnesia Test, high-velocity lead therapy (HVLT), digit span, and motor speed and dexterity is very useful in tracking recovery. NPE's value is also limited if a patient has other serious medical complications or psychiatric disorders.

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Information Obtained From Neuropsychological Reports

Neuropsychological tests are a series of measures that identify cognitive impairment and functioning in individuals. They provide quantifiable data about the following aspects of cognition:

Reasoning and problem-solving ability

Ability to understand and express language

Working memory and attention

Short-term and long-term memory

Processing speed

Visual-spatial organization

Visual-motor coordination

Planning, synthesizing, and organizing abilities

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Established Applications of Neuropsychological Evaluation

Applications of NPE include the following:

Provide a differential diagnosis of organic and functional pathologies

Developmental disorders (eg, specific learning disabilities) require detailed assessment of cognition, academic achievement, and psychosocial adjustment for proper identification and as a guide to their management. Academic placement in special education and resource classrooms may be needed.

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Patient-Specific Factors and Normative Data

Results of an NPE must be considered in the context of the patient’s age, education, sex, and cultural background. These factors can affect test performance and limit the conclusions that can be drawn from the evaluation. In addition, issues such as reliability, validity, sensitivity, and specificity need to be considered.

Large, population-based norms are available for relatively few measures. Those measures that do boast such norms, such as major intellectual and academic instruments, are of limited usefulness within a neuropsychological test battery. Ideally, patients should be compared with population-based norms, as well as with local norms and subgroup norms (ie, specific patient populations) to examine strengths and weaknesses. However, significant gaps can be found in the normative data for all age, educational, and intellectual ranges. Major deficiencies have also existed in the development of appropriate measures and norms for minority populations.
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A study by Hansson et al indicated that taking a collaborative and therapeutic (CTA) approach to NPE of pediatric patients with neurodevelopmental disorders can reduce the number of psychiatric symptoms reported by these patients. The study, of children with suspected neurodevelopmental disorders, utilized the Beck Youth Inventories (BYI). The investigators found that fewer psychiatric symptoms were reported on most BYI subscales by those children who were assessed with the CTA approach (11 patients) than by those whose needs were addressed through parent support measures (11 patients) and those on a waiting list for help (9 patients). At 6-month follow-up, the decrease in self-reported symptoms was still seen on the BYI anger and anxiety subscales.
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Reliability, Validity, Sensitivity, and Specificity

Reliability

Reliability refers to the consistency with which the same information is obtained via the test or set of tests. In the absence of intervening variables (eg, illness, injury, new learning), scores should remain stable even in the event of certain other variables, such as the following:

Interrater reliability - Administration of the test by different examiners

Intrarater reliability - Administration of the test by the same examiner on more than 1 occasion

Test-retest reliability - Administration of the test to the same patient on different occasions

Validity

Validity refers to how well the test measures what it purports to measure. Specific types of validity that may be questioned include the following:

Construct validity - Does the test measure what it is supposed to measure

Concurrent validity - Do new tests correlate highly with existing tests or independent measures of the construct in question

Face validity - Does the test appear to measure what it is supposed to measure

The amount of variance accounted for by cognitive factors alone, however, is typically quite small. Exceptions occur when comparisons made between results of formal NPE and real-world criteria are limited to very simple, very circumscribed, and/or very well-defined functions. Consequently, situational assessment is seen as a critical adjunct to neuropsychological assessment, especially at higher levels of cognitive functioning.

Neuropsychological tests, with very few exceptions, were not developed with an eye toward ecologic validity. They were developed as indicators of brain function or dysfunction and generally were validated against neurosurgical, neurologic, and neuroradiologic data. Nevertheless, many tests have proven to be good predictors of future behavior and, therefore, have demonstrated ecologic validity.

A qualitative process approach may improve the ecologic validity of the neuropsychological test battery. For example, testing the limits with measures of memory and executive functioning allows the examiner to understand better what a person can do under relatively ideal circumstances (not “what,” but “how”). The test itself may have little demonstrable ecologic validity, but an accurate analysis and insightful interpretation of findings can be highly valid from an ecologic perspective.

Using a survey of 654 members of the National Academy of Neuropsychology (NAN) and the International Neuropsychological Society, Hirst et al found evidence that neuropsychologists are not equally consistent in employing validity testing practices recommended by the NAN and the American Academy of Clinical Neuropsychology in neuropsychological assessments. The survey indicated that neuropsychologists who work with pediatric and geriatric patients tend to follow the recommendations less frequently than do those who work with nongeriatric adults. In addition, longer-practicing neuropsychologists tended more often not to follow validity testing recommendations than did those who have not been practicing as long.
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Sensitivity and specificity

Sensitivity refers to a test’s ability to detect the slightest abnormalities in CNS function and is a reflection of the test’s true positive rate, that is, its ability to identify persons with a disorder. Specificity refers to the ability to differentiate patients with a certain abnormality from those with other abnormalities or with no abnormality, as indicated by the true negative rate. A score on any test can be a true positive, false positive, true negative, or false negative. Such results signify the following:

True positive – Requires high sensitivity to dysfunction, allowing dysfunctions to be detected

False positive- Indicates sensitivity to dysfunction, but lacks specificity to a particular dysfunction

True negative- Requires high specificity, allowing negative to be distinguished from others

False negative- Indicates a lack of sensitivity, without regard to specificity of the test

For any evaluation, it is important to understand the rates of each of the 4 result categories. The Stroop Test, for example, shows a relatively high level of specificity, with a high true negative rate (95.7%) and low false positive rate (4.3%). However, its sensitivity is questionable, as it has a relatively low true positive rate (30.8%) and high false negative rate (69.2%).

Each test has strengths and weaknesses in its ability to detect a minimal CNS dysfunction (sensitivity) while being able to indicate a specific CNS dysfunction (specificity). Timed measures of cognitive and/or motor processing are generally sensitive to diffuse cerebral dysfunctions, although the specificity of these tests is generally poor to moderate. Measures of cognitive and/or motor processing that are not timed are generally less sensitive to diffuse dysfunctions but are very useful in identifying specific brain lesions.

Overcoming problems in assessing executive function

Perhaps the major drawback of NPE is the lack of ecologic validity when assessing executive functioning.
[22] NPE is generally conducted within calm and quiet testing rooms where the subject is clearly presented with the task to be completed, is informed of time restrictions, and is prompted to start and stop behaviors. Under these conditions, a subject may achieve a score that indicates no executive dysfunctions, although the individual may be particularly drained from the mental exertion. Completing tasks in the real world, however, requires several executive functions that are not tested in traditional NPE, including recognizing that a task must be completed, starting the task, switching tasks, adapting to changes, and stopping a task.

However, changes in executive tests have dramatically increased the environmental validity of executive NPE. These changes include a growing emphasis on subject self reporting of premorbid and postmorbid functioning, as well as premorbid and postmorbid reports from relatives and significant others in the subject’s life. Often, however, the self report is not sufficient, for executive dysfunctions may be unknown to the subject, or else they may be ego-syntonic.

A dramatic approach to overcoming the problem of ecologic validity is found in the Multiple Errands Test (MET). The test takes place in a shopping mall and requires the subject to conduct 3 tasks simultaneously, such as buying an item, meeting at a certain location at a certain time, and acquiring available information (such as a foreign currency exchange rate). This evaluation tests the subject’s abilities in planning, task initiation, and task switching, and even requires the subject to interact with other individuals in an effective manner. The test has shown considerable sensitivity and specificity, and subjects with neurologic deficits have performed considerably worse than controls. A version of this test has also been created for the hospital setting.